Composite Structure and Method for Inspecting a Pre-bond Surface of a Composite Structure

ABSTRACT

A composite structure may include a composite substrate, the composite substrate including a surface, a peel ply, the peel ply including a surface, and an identifiable marking agent, wherein the surface of the peel ply includes the identifiable marking agent, and wherein the peel ply is connected to the composite substrate such that the identifiable marking agent is in contact with the surface of the composite substrate.

FIELD

The present disclosure is generally related to composite structures and,more particularly, to composite structures having improved surfacebonding characteristics and methods for inspecting a pre-bond surface ofa composite structure to verify sufficient surface treatment forbonding.

BACKGROUND

Composite structures have an advantageous combination of high strengthand lightweight. As such, composite structures commonly find use inaerospace and other industries where such properties are beneficial. Forexample, the surface skins of modern aircraft may commonly be formed ofcomposite structures.

Composite structures include reinforcing fibers impregnated with a resinmatrix. Often, it may be necessary to attach the composite structure toanother structure, such as a second composite structure or an internalstructural support (e.g., a stiffener). The strength of the bond betweencomposite structures may depend on the surface characteristics of thecomposite structure.

Commonly, the surface of the composite structure may be relativelysmooth and exhibit relatively weak bonding strength and durability. As aresult, methods have been developed to increase the bonding strength anddurability of the surface of the composite structure. One such method isthe use of a peel ply during the manufacture of a composite structure. Apeel ply typically includes a sheet of dry woven fabric or a sheet ofwoven fabric impregnated with a resin matrix. The peel ply may be placedon an uncured surface of the composite structure. The compositestructure and the peel ply are then co-cured. Once cured, the peel plymay be removed from the surface of the composite structure. Once thepeel ply is removed, the surface of the composite structure may beroughened or textured.

Removal of the peel ply is intended to generate a clean surface readyfor bonding. A supplementary ablation surface treatment after removal ofthe peel ply, such as abrasion or plasma, may be required to ensureremoval of any peel ply residue that could impact bonding performance.Inspection of the pre-bond surface to verify complete removal of anyresidue transferred to the surface may also be required and can beexpensive and/or time consuming.

Accordingly, those skilled in the art continue with research anddevelopment efforts in the field of preparing a surface of a compositestructure for bonding and pre-bond surface inspection.

SUMMARY

In one embodiment, the disclosed composite structure may include acomposite substrate, the composite substrate including a surface, a peelply, the peel ply including a surface, and an identifiable markingagent, wherein the surface of the peel ply includes the identifiablemarking agent, and wherein the peel ply is connected to the compositesubstrate such that the identifiable marking agent is in contact withthe surface of the composite substrate.

In another embodiment, the disclosed peel ply structure may include apeel ply, the peel ply including a surface, and an identifiable markingagent, wherein the surface of the peel ply includes the identifiablemarking agent.

In yet another embodiment, also disclosed is a method for inspecting apre-bond surface of a composite structure, the method may include thesteps of: (1) providing a peel ply, the peel ply including a surface,and the surface of the peel ply including an identifiable marking agent,(2) placing the peel ply on a surface of a composite substrate, whereinthe surface of the peel ply is in contact with the surface of thecomposite substrate, (3) co-curing the peel ply and the compositesubstrate, (4) removing the peel ply from the composite substrate toform a modified surface of the composite substrate, (5) inspecting thecomposite substrate for the identifiable marking agent transferred tothe modified surface, wherein the identifiable marking agent is evidenceof residue transferred from the peel ply to the composite substrate, (6)ablating the modified surface to remove the identifiable marking agentand the residue and (7) subsequently re-inspecting the modified surfaceafter the ablating step for the identifiable marking agent and verifyingthat the modified surface is clean of residue transferred from the peelply to the composite substrate during the co-curing process.

Other embodiments of the disclosed composite structure and method forpreparing a composite structure for bonding will become apparent fromthe following detailed description, the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the disclosed composite structure;

FIG. 2 is a schematic illustration of the disclosed composite structureof FIG. 1 showing the peel ply being removed from the compositesubstrate;

FIG. 3 is a schematic illustration of one embodiment of the disclosedcomposite structure;

FIG. 4 is a plan view of one embodiment of the peel ply of the disclosedcomposite structure of FIG. 3;

FIG. 5 is a schematic illustration of the disclosed composite structureof FIG. 3 depicting the composite substrate after removal of the peelply;

FIG. 6 is a schematic illustration of another embodiment of thedisclosed composite structure;

FIG. 7 is a schematic illustration of the disclosed composite structureof FIG. 6 depicting the composite substrate after removal of the peelply;

FIG. 8 is a schematic illustration of the disclosed composite structureafter removal of identifiable marking agent and residue from the surfaceof the composite substrate;

FIG. 9 is a block diagram illustrating one embodiment of the disclosedmethod for inspecting a pre-bond surface of a composite structure;

FIG. 10 is flow diagram of an aircraft production and servicemethodology; and

FIG. 11 is a block diagram of an aircraft.

DETAILED DESCRIPTION

The following detailed description refers to the accompanying drawings,which illustrate specific embodiments of the disclosure. Otherembodiments having different structures and operations do not departfrom the scope of the present disclosure. Like reference numerals mayrefer to the same element or component in the different drawings.

Referring to FIG. 1, one embodiment of the disclosed compositestructure, generally designated 10, may include a composite substrate 12and a peel ply 14. The composite substrate 12 may include opposed planarsurfaces 24 and 26. The peel ply 14 may include opposed planar surfaces44 and 46. The peel ply 14 may be applied (e.g., connected) to thecomposite substrate 12 such that the surface 44 of the peel ply 14 is incontact with the surface 24 (e.g., a top surface of a single layer ofcomposite substrate or a top surface of an upper most compositesubstrate of a plurality of layers of composite substrate) of an uncuredor partially cured composite substrate 12. The peel ply 14 together withthe composite substrate 12 may be subjected to co-curing to form thecomposite structure 10.

Referring to FIG. 2, once the composite substrate 12 and the peel ply 14have been co-cured, the peel ply 14 may be removed (e.g., peeled) fromthe surface 24 of the composite substrate 12. The peel ply 14 may modifyto the surface 24 thereby forming a modified surface 28. For example,the surface 44 of the peel ply 14 may provide a modified surface 28 ofthe composite substrate 12 having an increased surface area, a roughenedor textured surface and/or a chemically active resin ready for bondingwith another structure, such as a second composite substrate (notshown). The peel ply 14 may leave residue 30 on the modified surface 28of the composite substrate 12. For example, the residue 30 may includeparticles or other remnants transferred from the surface 44 of the peelply 14 to the modified surface 28.

The characteristics of the modified surface 28 of the compositesubstrate 12 created by removal of the peel ply 14 may be directlyinfluenced by how the peel ply 14 separates from the composite substrate12. For example, a fracture line (not shown) during peeling of the peelply 14 may be within the composite substrate 12 or at the interfacebetween the surface 44 of the peel ply 14 and the surface 24 of thecomposite substrate 12, thus forming the modified surface 28.

For example, complete removal of the peel ply 14 from the surface 24 ofthe composite substrate 12 may modify the surface 24 of the compositesubstrate 12 (e.g., forming the modified surface 28) so as to facilitateand promote stronger and longer lasting bonding between the modifiedsurface 28 of the composite substrate 12 and a second compositesubstrate.

As another example, incomplete removal of the peel ply 14 may transferresidue 30 on to the modified surface 28 after the peel ply 14 has beenremoved. The residue 30 may create weak bonds between the modifiedsurface 28 of the composite substrate 12 and a second compositesubstrate. Those skilled in the art will appreciate that incompleteremoval of the peel ply 14 is not uncommon.

Referring to FIGS. 3 and 6, illustrating the composite structure 10after co-curing of the composite substrate 12 and the peel ply 14. Thecomposite substrate 12 may include any suitable fiber-reinforced resincomposite substrate (e.g., fiber-reinforced polymer). The compositesubstrate 12 may include fibers 16 (e.g., reinforcing fibers) embeddedor impregnated in a resin matrix 18.

In an example implementation of the composite substrate 12, the resinmatrix 18 may be in contact with the fibers 16 but not impregnated inthe fibers 16. As another example implementation, the resin matrix 18may be partially embedded or partially impregnated in the fibers 16. Asyet another example implementation, the resin matrix 18 may be fullyembedded or fully impregnated in the fibers 16.

As a specific, non-limiting example, the composite substrate 12 mayinclude a prepreg (e.g., a single layer of composite substrate 12) orprepreg layups (e.g., a plurality of layers of composite substrate 12),such as those conventionally used in the manufacturing of structuralparts in the aerospace, automotive and marine industries.

The fibers 16 may be selected from any suitable material including, butnot limited to, glass (e.g., glass-reinforced polymer), carbon (e.g.carbon-fiber-reinforced polymer), graphite, and polymer fibers. Anycombination of fibers 16 may be selected. The fibers 16 may be cracked(e.g., stretch-broken) fibers, discontinuous fibers, or continuousfibers. The fibers 16 may be in the form of woven, non-crimped,non-woven, unidirectional, or multiaxial textile tapes or tows (e.g., afiber layer).

The resin matrix 18 may include any suitable polymeric resin. When curedor partially cured, the resulting resin matrix 18 may form across-linked matrix of polymeric resin. For example, the resin matrix 18may include any thermosetting or thermoplastic resin.

Suitable thermoset resin materials may include, but are not limited to,phenol formaldehyde, urea-formaldehyde, 1,3,5-triazine-2,4,6-triamine(melamine), bismaleimide (BMI), epoxies, vinyl esters, benzoxazines,phenolics, polyesters, unsaturated polyesters, cyanate esters, acombination of any two or more thereof or any other suitable resinmaterial.

Suitable thermoplastic resins materials may include, but are not limitedto, polyether sulfone (PES), polyether ethersulfones (PEES), polyphenylsulfones (PPS), polysulfones (PSU), polyesters, polymerizablemacrocycles (e.g., cyclic butylene terephthalate), liquid crystalpolymers, polyimides, polyetherimides (PEI), aramids, polyamides,polyketones, polyetheretherketone (PEEK), polyetherketoneketone (PEKK),polyurethanes, polyureas, polyarylethers, polyarylsulfides,polycarbonates, polyphenylene oxide (PPO) and modified PPO, acombination of any two or more thereof or any other suitable resinmaterial.

The composite structure 10 may include at least one curing agent. Forexample, the curing agent may be present in the resin matrix 18 (e.g.,the polymeric resin). Suitable curing agents may include, but are notlimited to, cyanoguanidine, aromatic amines, aliphatic amines, acidanhydrides, Lewis acids, substituted ureas, imidazoles, hydrazines,amides, substituted amides, imines, substituted imines, hydrazides, acombination of any two or more thereof or any other suitable curingagent.

The composite substrate 12, the resin matrix 18 and/or the fibers 16 mayalso include additional ingredients, such as performance enhancing ormodifying agents. For example, the performance enhancing or modifyingagents may include, but are not limited to, flexibilizers, tougheningagents or particles, accelerators, flame retardants, wetting agents,pigments or dyes, plasticizers, UV absorbers, anti-fungal compounds,fillers, viscosity modifiers, flow control agents, tackifiers,stabilizers, inhibitors, or any combination of two or more thereof.

Referring still to FIGS. 3 and 6, the peel ply 14 may include a fabriclayer 38. Opposed surfaces of the fabric layer 38 may define the opposedplanar surfaces 44 and 46 of the peel ply 14. The peel ply 14 may be awet peel ply 14 (e.g., the fabric layer 38 is pre-impregnated with aresin matrix) or a dry peel ply 14 (e.g., the fabric layer 38 is free ofa resin matrix).

The fabric layer 38 may be a woven fabric. For example, the fabric layer38 may include a plurality of yarns 48 woven in a weaving pattern. Eachyarn 48 may include a plurality of continuous fibrous filaments 20(e.g., single fibers) twisted together. For example, each yarn 48 mayinclude between approximately 28 to 48 filaments 20 twisted together.Only a portion of a single yarn 48 is shown in FIGS. 3-6.

The filaments 20 may be any suitable material including, but not limitedto, polyesters, polyethylene terephthalate (PET), polybutyleneterephthalate (PBT), polytrimethylene terephthalate (PTT), polylacticacid, polyethylene, polypropylene, nylons, elastomeric materials (e.g.,LYCRA®), polyaramids (e.g., high-performance fibers), para-aramids (e.g.KEVLAR®), meta-aramids (e.g. NOMEX®), polyimides, polyetheretherketone(PEEK), glass or any other suitable material.

In an example implementation of a wet peel ply 14, the fabric layer 38may be impregnated with a resin matrix (not shown). The resin matrix mayinclude any suitable polymeric resin. The resin matrix of the peel ply14 may be the same as or different from the resin matrix 18 of thecomposite substrate 12. As a general, non-limiting example, the resinmatrix of the peel ply 14 may be a DGEBA epoxy and the resin matrix 18of the composite substrate 12 may be another compatible epoxy resin.

During a co-curing process, the resin matrix 18 of the compositesubstrate 12 may impregnate with fabric layer 38 but not bond with thefabric layer 38 such that the peel ply 14 may be removed from thesurface 24 of the composite substrate 12 to form the modified surface28.

The surface 44 of the peel ply 14 may include an identifiable markingagent 32. For example, the identifiable marking agent 32 may be appliedonto the surface 44 of the peel ply 14 or incorporated into the peel ply14 (e.g., into the fabric layer 38) defining at a portion of the surface44 of the peel ply 14. The identifiable marking agent 32 may be selectedto afford high visual discernibility with respect to the peel ply 14and/or the composite substrate 12. As an example, when the fabric layer38 of the peel ply 14 and/or the resin matrix 18 of the compositesubstrate 12 are dark in color, the identifiable marking agent 32 may belight (e.g., bright) and/or contrasting in color. As another example,when the fabric layer 38 of the peel ply 14 and/or the resin matrix 18of the composite substrate 12 are light in color, the identifiablemarking agent 32 may be dark and/or contrasting in color. As stillanother example, the identifiable marking agent 32 may include one ormore components that are chemically activated (e.g., fluorescent),mechanically activated, or light activated (e.g., UV active) prior to anablation process, as described in more detail herein below.

Referring to FIG. 3, in an example embodiment, the identifiable markingagent 32 may be applied to the surface 44 of the peel ply 14. Forexample, the identifiable marking agent 32 may be applied onto at leasta portion of the surface 44 of the peel ply 14 that is placed in contactwith the surface 24 of the composite substrate 12. As an example, theidentifiable marking agent 32 may be applied to and cover a portion ofthe fabric layer 38 defining the surface 44. For example, theidentifiable marking agent 32 may cover at least a portion of a surface34 of one or more filaments 20 that are in contact with the surface 24of the composite substrate 12. Thus, an identifiable marking layer 36may be positioned between at least a portion of the fabric layer 38(e.g., one or more filaments 20) of the peel ply 13 and the surface 24of the composite substrate 12.

In an example implementation, the identifiable marking agent 32 may beink, fiber dye, or any other visible marking agent. For example, theidentifiable marking agent 32 (e.g., ink) may be applied to the surface44 of the peel ply 14 (e.g., at least a portion of the fabric layer 38defining the surface 44) with a roller, a printer (e.g., an inkjetprinter), or any other suitable application device. In a wet peel plyexample, the identifiable marking agent 32 may be applied to the surface44 of the peel ply 14 after heat setting.

As a general, non-limiting example, the identifiable marking agent 32may be ink 54 suitable for application (e.g., printing) onto the peelply 14. As a specific, non-limiting example, the ink 54 may be polyesterresin based ink suitable for application onto a polyester peel ply. Asanother specific, non-limiting example, the ink 54 may be nylon resinbased ink suitable for application onto a nylon peel ply.

The ink 54 (e.g., the identifiable marking agent 32) may be applied atany suitable thickness t. The thickness t may be selected to limitcontamination of the modified surface 28. As an example, the ink 54 maybe applied at a thickness t of between approximately 25 nm to 200 nm. Asanother example, the ink 54 may be applied at a thickness t of betweenapproximately 50 nm to 150 nm. As another example, the ink 54 may beapplied at a thickness t of between approximately 50 nm to 100 nm.

The surface area (e.g., of the surface 44) covered by the ink 54 (e.g.,the identifiable marking agent 32) may be optimized to limit additionalcontamination to the modified surface 28 of the composite substrate 12.As an example, the ink 54 may cover at most 5% of the surface 44 of thepeel ply 14. As another example, the ink 54 may cover at most 10% of thesurface 44 of the peel ply 14. As another example, the ink 54 may coverat most 25% of the surface 44 of the peel ply 14. As another example,the ink 54 may cover at most 50% of the surface 44 of the peel ply 14.As yet another example, the ink 54 may cover 100% of the surface 44 ofthe peel ply 14.

Referring to FIG. 4, the ink 54 (e.g., the identifiable marking agent32) may be applied to the surface 44 of the peel ply 14 (e.g., at leasta portion of the surface 34 of one or more filaments 20) in any suitablepattern. For example, the ink 54 may be applied to the surface 44 of thepeel ply 14 in a grid pattern 50 (e.g., a print array). As a specific,non-limiting example, the ink 54 may be applied to the surface 44 of thepeel ply 14 in a grid pattern 50 defined by approximately 25 cm squares.Those skilled in the art will appreciate the dimensions of the squaresdefining the grid pattern 50 may depend upon various factors including,but not limited to, the dimensions of the peel ply 14.

Referring to FIG. 5, following co-curing of the composite substrate 12and the peel ply 14 and removal of the peel ply 14 from the compositesubstrate 12, residue 30 from the peel ply 14 may remain on the modifiedsurface 28 of the composite substrate 12. The residue 30 may includeparticles, contamination, and/or any other residue remaining (e.g.,transferred) from the peel ply 14 to the modified surface 28 followingremoval of the peel ply 14. For example, the residue 30 may includeremnants from the filaments 20 (e.g., portions of the fabric layer 38).

At least some of the identifiable marking agent 32 may also betransferred to the modified surface 28 of the composite substrate 12along with any residue 30 upon removal of the peel ply 14. As shown inFIG. 5, the identifiable marking agent 32 is depicted as ink 54 appliedto the surface 44 of the peel ply 14 (e.g., at least a portion of thesurface 34 of one or more filaments 20). Following removal of the peelply 14, any transferred residue 30 may be layered on top of the ink 54(e.g., identifiable marking agent 32), thus the ink 54 may be positionedbetween the residue 30 and the modified surface 28. The ink 54 may bevisible on the modified surface 28 upon removal of the peel ply 14.Inspection (e.g., visual inspection) of the modified surface 28 mayreadily identify the existence of any residue 30 evidenced by theexistence of the ink 54 (e.g., identifiable marking agent 32) on themodified surface 28.

Referring to FIG. 6, in another example embodiment, the identifiablemarking agent 32 may be incorporated into the peel ply 14 defining atleast a portion of the surface 44. For example, the identifiable markingagent 32 may be a plurality of tracer filaments 52. The plurality oftracer filaments 52 and the plurality of filaments 20 may be twistedtogether to form at least a portion of the yarns 48 that are woven toform the fabric layer 38. The yarns 48 may be configured such that thetracer filaments 52 are disposed at the surface of the fabric layer 38that is placed in contact with the surface 24 of the composite substrate12 (e.g., defining at least a portion of the surface 44 of the peel ply14). Thus, an identifiable marking layer 36 (e.g., a plurality of tracerfilaments 52) may be positioned in contact with the surface 24 of thecomposite substrate 12 (e.g., between a portion of the fabric layer 38and the surface 24 of the composite substrate 12).

In an example implementation, the identifiable marking agent 32 may be aplurality of tracer filaments 52 having a different and/or contrastingcolor with respect to the remaining filaments 20 of the yarn 48. Whenthe surface 44 of the peel ply 14 is applied to the surface 24 of thecomposite substrate 12, a plurality of tracer filaments 52 may extendacross the surface 24 in one or more directions.

The tracer filaments 52 (e.g., the identifiable marking agent 32) maydefine at least a portion of the surface 44 of the peel ply 14. As anexample, the tracer filaments 52 may define at most 5% of the surface 44of the peel ply 14. As another example, the tracer filaments 52 maydefine at most 10% of the surface 44 of the peel ply 14. As anotherexample, the tracer filaments 52 may define at most 25% of the surface44 of the peel ply 14. As another example, the tracer filaments 52 maydefine at most 50% of the surface 44 of the peel ply 14. As yet anotherexample, the tracer filaments 52 may define 100% of the surface 44 ofthe peel ply 14.

Referring to FIG. 7, following co-curing of the composite substrate 12and the peel ply 14 and removal of the peel ply 14 from the compositesubstrate 12, residue 30 from the peel ply 14 may remain on the modifiedsurface 28 of the composite substrate 12. The residue 30 may includeparticles, contamination, and/or any other residue remaining (e.g.,transferred) from the peel ply 14 to the modified surface 28 followingremoval of the peel ply 14. As an example, the residue 30 may includeremnants from the tracer filaments 52. As another example, the residue30 may include remnants from the tracer filaments 52 and residue fromthe filaments 20 layered on top of the tracer filaments 52 (e.g.,portions of the fabric layer 38).

At least some of the identifiable marking agent 32 may also betransferred to the modified surface 28 of the composite substrate 12along with any residue 30 upon removal of the peel ply 14. As shown inFIG. 7, the identifiable marking agent 32 is depicted as tracerfilaments 52 incorporated into the peel ply 14 defining at least aportion of the surface 44. Following removal of the peel ply 14, anytransferred residue 30 may be layered on top of the tracer filaments 52(e.g., identifiable marking agent 32), thus the tracer filaments 52 maybe positioned between the residue 30 and the modified surface 28. Thetracer filaments 52 (e.g., the identifiable marking agent 32) may bevisible on the modified surface 28 upon removal of the peel ply 14.Inspection (e.g., visual inspection) of the modified surface 28 mayreadily identify the existence of any residue 30 evidenced by theexistence of the tracer filaments 52 (e.g., identifiable marking agent32) or remnants of the tracer filaments 52 on the modified surface 28.

Referring to FIG. 8, an ablation device 40 may be used to prepare themodified surface 28 of the composite substrate 12 following removal ofthe peel ply 14 (not shown in FIG. 8). The ablation device 40 mayperform surface ablation to a depth d suitable to completely remove anyresidue 30 transferred from the peel ply 14 (e.g., the fabric layer 38)and remaining on the modified surface 28 of the composite substrate 12.The depth d may be defined by the depth required to completely removethe identifiable marking agent 32 (e.g., ink 54 or tracer filaments 52)visible on the modified surface 28.

Thus, surface ablation of a depth d suitable to remove substantially allof the visible identifiable marking agent 32 may provide visual evidenceof removal of substantially all of the residue 30 and leave the modifiedsurface 28 ready for bonding with a second composite substrate. Theablation device 40 may be any suitable ablation device 40, such as aplasma, laser or grit blast ablation device.

Referring to FIG. 9, one embodiment of the disclosed method, generallydesignated 100, for inspecting a pre-bond surface of a compositestructure may begin at block 102 by providing a composite substrate. Thecomposite substrate may include reinforcing fibers impregnated with aresin matrix. The composite substrate may include a surface to beprepared for bonding.

As shown at block 104, a peel ply may be provided. The peel ply mayinclude a fiber layer. The fabric layer may include a plurality offilaments twisted and/or woven together.

As shown at block 106, an identifiable marking agent may be incorporatedto a surface of the peel ply. As an example, the identifiable markingagent may be incorporated onto the surface of the fiber layer of thepeel ply (e.g., ink applied onto the surface of the fabric layer). Asanother example, the identifiable marking agent may be incorporated intothe surface of the fiber layer of the peel ply (e.g., tracer filamentswoven into the fabric layer).

As shown at block 108, the peel ply may be placed on the compositesubstrate such that the surface of the peel ply (e.g., a surface of thefabric layer) having the incorporated identifiable marking agent is incontact with the surface of the composite substrate (e.g., theidentifiable marking agent is disposed between the fabric layer and thesurface of the composite substrate).

As shown at block 110, the composite substrate and the peel ply may beco-cured.

As shown at block 112, the peel ply may be removed from the compositesubstrate. The peel ply may be removed from the surface of the compositesubstrate to form a modified surface.

As shown at block 114, the modified surface of the composite substratemay be inspected to detect if any of the identifiable marking agent wastransferred to the composite substrate following removal of the peelply. For example, the modified surface of the composite substrate may bevisually inspected. In an example implementation, visual inspection maybe performed manually. In another example implementation, visualinspection may be performed by a machine based vision inspection system.For example, the vision inspection system may implement automatedresidue identification software.

Any residue transferred to the modified surface of the compositesubstrate may be detected (e.g., visually identified) by the existenceof the identifiable marking agent on the modified surface. Thus, theidentifiable marking agent may provide visible evidence of residuetransferred to the modified surface following removal of the peel ply.

As shown at block 116, the modified surface may be ablated to remove theidentifiable marking agent, and thus any residue transferred from thepeel ply to the surface of the composite substrate. Surface ablation maybe performed to a depth suitable to remove the entire identifiablemarking agent from the modified surface, and thus also removing anyresidue disposed on top of the ink.

As shown at block 118, the modified surface of the composite substratemay be visually inspected to ensure that substantially all of theidentifiable marking agent transferred to the composite substrate hasbeen eliminated, and thus ensuring that substantially all of the residuetransferred to the composite substrate has been removed.

Accordingly, the disclosed composite structure and method for preparinga composite structure for bonding may include incorporation of anidentifiable marking agent to a surface of peel ply (e.g., a fabriclayer of the peel ply). The identifiable marking agent may be designedto transfer to a composite substrate and be visible upon removal of thepeel ply. Transfer of any residue from the peel ply that occurs duringremoval of the peel ply may be readily identifiable by the identifiablemarking agent, thus allowing for visual inspection of the modifiedsurface of the composite substrate to identify any residue on thesurface. Surface ablation may be performed to a depth suitable to removethe identifiable marking agent (e.g., substantially all of theidentifiable marking agent). Removal of the identifiable marking agent(e.g., substantially all of the identifiable marking agent) from thesurface of the composite substrate may provide visual evidence that theresidue (e.g., substantially all of the residue) has been removed.

Examples of the disclosure may be described in the context of anaircraft manufacturing and service method 200, as shown in FIG. 10, andan aircraft 202, as shown in FIG. 11. During pre-production, theaircraft manufacturing and service method 200 may include specificationand design 204 of the aircraft 202 and material procurement 206. Duringproduction, component/subassembly manufacturing 208 and systemintegration 210 of the aircraft 202 takes place. Thereafter, theaircraft 202 may go through certification and delivery 212 in order tobe placed in service 214. While in service by a customer, the aircraft202 is scheduled for routine maintenance and service 216, which may alsoinclude modification, reconfiguration, refurbishment and the like.

Each of the processes of method 200 may be performed or carried out by asystem integrator, a third party, and/or an operator (e.g., a customer).For the purposes of this description, a system integrator may includewithout limitation any number of aircraft manufacturers and major-systemsubcontractors; a third party may include without limitation any numberof venders, subcontractors, and suppliers; and an operator may be anairline, leasing company, military entity, service organization, and soon.

As shown in FIG. 11, the aircraft 202 produced by example method 200 mayinclude an airframe 218 with a plurality of systems 220 and an interior222. Examples of the plurality of systems 220 may include one or more ofa propulsion system 224, an electrical system 226, a hydraulic system228, and an environmental system 230. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosed composite structure 10 and method 100 may be applied to otherindustries, such as the automotive industry.

Apparatus and methods embodied herein may be employed during any one ormore of the stages of the production and service method 200. Forexample, components or subassemblies corresponding tocomponent/subassembly manufacturing 208, system integration 210, and ormaintenance and service 216 may be fabricated or manufactured using thedisclosed composite structure 10 and method 100. Also, one or moreapparatus examples, method examples, or a combination thereof may beutilized during component/subassembly manufacturing 208 and/or systemintegration 210, for example, by substantially expediting assembly of orreducing the cost of an aircraft 202, such as the airframe 218 and/orthe interior 222. Similarly, one or more of apparatus examples, methodexamples, or a combination thereof may be utilized while the aircraft202 is in service, for example and without limitation, to maintenanceand service 216.

Although various embodiments of the disclosed composite structure andmethod for preparing a composite structure for bonding have been shownand described, modifications may occur to those skilled in the art uponreading the specification. The present application includes suchmodifications and is limited only by the scope of the claims.

1. A composite structure comprising: a composite substrate, saidcomposite substrate comprising a surface; a peel ply, said peel plycomprising a surface; and an identifiable marking agent, wherein saidsurface of said peel ply comprises said identifiable marking agent, andwherein said peel ply is connected to said composite substrate such thatsaid identifiable marking agent is in contact with said surface of saidcomposite substrate.
 2. The composite structure of claim 1 wherein saididentifiable marking agent is applied onto said surface of said peelply.
 3. The composite structure of claim 2 wherein said identifiablemarking agent comprises ink.
 4. The composite structure of claim 3wherein said peel ply comprises a fabric layer, and wherein said ink isapplied to at least a portion of a surface of said fabric layer.
 5. Thecomposite structure of claim 3 wherein said ink comprises a resin basedink compatible with said fabric layer.
 6. The composite structure ofclaim 3 wherein said ink comprises a thickness, said thickness beingapproximately between 50 nm and 100 nm.
 7. The composite structure ofclaim 3 wherein said ink is applied onto said surface of said peel plyin a grid pattern.
 8. The composite structure of claim 1 wherein saididentifiable marking agent is incorporated into said surface of saidpeel ply.
 9. The composite structure of claim 8 wherein saididentifiable marking agent comprises a plurality of tracer filaments.10. The composite structure of claim 9 wherein said peel ply comprises afabric layer, and wherein said plurality of tracer filaments are woveninto said fabric layer to define at least a portion of said surface ofsaid peel ply.
 11. A peel ply structure comprising: a peel ply, saidpeel ply comprising a surface; and an identifiable marking agent,wherein said surface of said peel ply comprises said identifiablemarking agent.
 12. The peel ply structure of claim 11 wherein saididentifiable marking agent is applied onto said surface of said peelply.
 13. The peel ply structure of claim 12 wherein said peel plycomprises a fabric layer, wherein said identifiable marking agentcomprises ink, and wherein said ink is applied onto at least a portionof a surface of said fabric layer.
 14. The peel ply structure of claim11 wherein said identifiable marking agent is incorporated into saidsurface of said peel ply.
 15. The peel ply structure of claim 14 whereinsaid peel ply comprises a fabric layer, wherein said identifiablemarking agent comprises a plurality of tracer filaments, and whereinsaid plurality of tracer filaments are woven into said fabric layer todefine at least a portion of said surface of said peel ply.
 16. A methodfor inspecting a pre-bond surface of a composite structure, said methodcomprising: providing a peel ply, said peel ply comprising a surface,and said surface of said peel ply comprising an identifiable markingagent; placing said peel ply on a surface of a composite substrate,wherein said surface of said peel ply is in contact with said surface ofsaid composite substrate; co-curing said peel ply and said compositesubstrate; removing said peel ply from said composite substrate to forma modified surface of said composite substrate; and inspecting saidcomposite substrate for said identifiable marking agent transferred tosaid modified surface, wherein said identifiable marking agent isevidence of residue transferred from said peel ply to said compositesubstrate.
 17. The method of claim 16 comprising: ablating said modifiedsurface to remove said identifiable marking agent and said residue; andinspecting said modified surface after said ablating step for saididentifiable marking agent.
 18. The method of claim 16 comprisingapplying said identifiable marking agent onto said surface of said peelply.
 19. The method of claim 18 wherein said applying step comprisesapplying ink onto at least a portion of a surface of a fabric layer ofsaid peel ply.
 20. The method of claim 16 comprising incorporating saididentifiable marking agent into said surface of said peel ply.
 21. Themethod of claim 20 wherein said incorporating step comprises weaving aplurality of tracer filaments into a fabric layer of said peel ply todefine at least a portion of said surface of said peel ply.